Normally, when a downhole pump is to be removed for servicing or replacement, the well must be “killed” (i.e. prevent the well from flowing). The downhole tool of the present invention allows for direct sealing attachment to a downhole assembly in order for the well to be temporarily sealed downhole to allow the removal of a downhole pump for servicing or replacement without the need to remove the downhole assembly (e.g. a gas separator).
Specifically, when extracting hydrocarbons from production wells drilled into hydrocarbon formations, it is a safety and regulatory requirement that pressurized fluids and/or gases coming from the drilled well (e.g. sour gases), be isolated from surface to thereby prevent their escape to atmosphere at the surface of the well.
Accordingly, downhole pump assemblies typically possess seal rings, which when the pump is installed in the operative position, typically engage circumferential seals within the casing or tubing in which the downhole pump assembly was placed and positioned, thereby preventing pressurized fluids and/or gases from flowing to surface except through the pump and thereby through the production tubing.
However, any raising of the downhole pump for the purposes of repair or replacement, as taught in the prior art, necessarily disengages the sealing rings, thereby releasing the downhole pressurized fluids and/or gases to surface.
To avoid this undesirable situation and to avoid communication with surface when a downhole pump assembly is being replaced, the prior art teaches that a well be effectively “killed” prior to pump removal, typically by pumping viscous fluids downhole to temporarily seal the well prior to blowout preventer installation and the pump being removed.
The process of “killing” a well each time to service downhole components is costly and time-consuming. Additionally, in some instances, the “killing” process may be too effective where it becomes difficult, and sometimes impossible, to later “restore” the well by removing the viscous fluids. Therefore, a well that is temporarily killed may unintentionally be permanently killed or unable to be brought back on-stream as effectively as before.
In heavy oil formations, where the produced oil contains large amounts of abrasive sand, wear on the pumps is extensive. This results in the necessity to frequently replace the pumps. As described above, replacing the pumps results in the undesirable need in the prior art to “kill” the well so that pressurized fluids and/or gases deep in the formation are not otherwise allowed to flow directly to surface.
Applicant's commonly-assigned U.S. Pat. No. 8,893,776 disclosed a pump assembly for removing hydrocarbons from downhole wells without the need to “kill” the well. The apparatus disclosed therein involved a ported sleeve whereby in an operative first position, fluid is drawn from the well through a first port means in the sidewall of the sleeve, through the hollow interior of the sleeve, and out of the sleeve into the production tubing through a second port means near the upper end. In a closed second position, the ported sleeve shifts upwardly to position the first port means between two sets of seal means within a seal sub that surrounds the ported sleeve, thus sealing off the flow of fluid upwards in the well by preventing access to the lower (first) sidewall port means.
In an alternative design, Applicant's commonly-assigned U.S. Pat. No. 8,889,316 disclosed a downhole isolation tool having a ported sliding sleeve that is slidably positioned within a seal sub that has a port means. In an operative first position, the sliding sleeve is positioned within a bore of the seal sub such that an aperture means in the sidewall of the sleeve is aligned with the port means on the seal sub, allowing fluids to pass from an exterior surface of the seal sub into an elongate cavity within the sleeve. The fluids pass through a hollow internal cavity in the sleeve and out into the production tubing through a second aperture means near the upper end. In a closed second position, the sliding sleeve is moved upwards such that a seal member within the sliding sleeve is aligned with the port means on the seal sub, blocking fluids from the surrounding exterior from entering the sleeve.
These downhole tools provide significant benefits in downhole drilling operations for reasons described above in avoiding the need to “kill” the well prior to pump removal. The isolation tools are particularly well suited for sealing the flow of oil and gas through production tubing and permitting removal of a pump for repair or replacement.
In oil and gas reservoirs, petroleum oil is frequently found in intimate association with natural gas and water. Natural gas may, for instance, be in the form of free gas bubbles entrained in the oil and/or in the form of dissolved gas in the oil. Thus, well fluids commonly comprise both liquids and gas. In wells where artificial lift (pumping) is necessary, the presence of a gas-liquid mixture can materially affect the efficiency of the pumping operations. For example, gas presence in the pumping zone can cause problems such as gas lock, gas pound and gas interference.
Specifically, the presence of gas can reduce pump efficiency because, when gas enters the pump with oil, gas causes many pump problems. It may pocket around the pump or accumulate inside the pump and “gas lock” the valves. “Gas pound” can occur when the gas breaks out of solution and occupies a part of the pump intake chamber. The pump plunger will compress the gas during the down stroke and then contact the fluid. The presence of gas provides some amount of cushion, but the pump can still experience a sudden shock upon striking the fluid, causing “gas pound” followed by “fluid pound”. This phenomenon can cause significant damage to the pump assembly and rod string, such as rod buckling, rods rubbing against the tubing causing leaks and, in severe conditions, the splitting of the barrel and/or cages. Attacking downhole gas can reduce pump failures and maximize pump efficiency.
Specialized production equipment is commonly used in oil wells to mitigate damage. In wells where bubbles of gas are present, it is known in the art to use a gas separator (a.k.a. degasser, gas anchor or gas break assembly) to continuously separate the gas from the liquids before the liquid enters the inlet of the pump—the liquids being directed to the suction inlet of the pump and the gas being directed to the casing annulus. Therefore, the gas separator is typically fluidly coupled to the suction inlet of the rod pump, and is therefore located immediately below the rod pump. The efficiency of the separation of liquid and gas by the gas separator is an important aspect of gas separator design, and no gas separator is totally effective in this separation process. Thus, pump repair or replacement is still often required.
Moreover, gas separators frequently become plugged themselves and require that the entire gas separator assembly, or components thereof, be removed from the well for cleaning. This is particularly the case in wells drilled in heavy oil formations, where the produced oil contains large amounts of abrasive sand. It is not uncommon for sand to plug the inlet slots of the dip tube of a gas separator assembly, thereby necessitating removal and cleaning or replacement of the gas separator. Similar to the removal of a pump for repair or replacement, replacing the gas separator results in the undesirable need to “kill” the well so that pressurized fluids and/or gases deep in the formation are not otherwise allowed to flow directly to surface.
In wells equipped with such equipment (e.g. a gas separator) a real need exists for a specialized apparatus and method that is directly compatible with the downhole assemblies and which allows for removing worn or defective pumps without the need to first “kill” the well, and/or is able to avoid the undesirable release of pressurized fluids and/or gases from within the formation to surface via the open well. A need also exists for a downhole tool that permits the cleaning of a downhole assembly, e.g. a gas separator, without the need to remove the assembly and “kill” the well.